Non-compliant medical balloons for performing angioplasty and other medical procedures are known. U.S. Pat. No. 6,746,425 to Beckham discloses a non-compliant medical balloon and methods for manufacturing the balloon. U.S. Patent Application Publication No. US 2006/0085022 to Hayes et al. discloses a non-compliant medical balloon having an integral woven fabric layer and methods for manufacturing the balloon. U.S. Patent Application Publication No. US 2006/0085023 to Davies, Jr. et al. discloses a medical balloon having strengthening rods and methods for manufacturing the balloon. U.S. Patent Application Publication No. US 2006/0085024 to Pepper et al. discloses a non-compliant medical balloon having an integral non-woven fabric layer and methods for manufacturing the balloon. U.S. Pat. No. 6,746,425 and Publication Nos. US 2006/0085022, US 2006/0085023 and US 2006/0085024 are hereby incorporated herein by reference.
Medical balloons are widely used in a variety of medical procedures. Typically, an uninflated medical balloon is inserted into a body-space, e.g., blood vessel, urological vessel, etc. by means of a catheter. After positioning at the desired location within the body, the medical balloon may be inflated by introducing a pressurized fluid into the balloon through the catheter. The pressurized fluid causes the medical balloon to expand, and the adjacent body-space is similarly expanded. The fluid may then be withdrawn from the balloon, causing it to collapse to facilitate its removal from the body. Medical balloons are also used for temporarily occluding vessels, placing medical devices such as stents, drug delivery and heat transfer.
Medical balloons are generally referred to as compliant, non-compliant and semi-compliant. Balloon compliance is a term used to describe the change in a balloon's diameter as a function of pressure. Low pressure compliant medical balloons are typically formed from elastomers such as latex, polyurethane and other thermoplastic elastomers. Low pressure compliant medical balloons may expand by 100% or greater upon inflation. Compliant medical balloons are typically used for fixation and occlusion.
Alternatively, high pressure non-compliant dilation balloons expand very little, if at all, when pressurized from a nominal diameter to a rated burst pressure. The rated burst pressure is the maximum pressure at which there is a statistical 95% confidence level that 99.9% of the population of balloons will not burst. High pressure non-compliant balloons may have rated burst pressures of up to 20 atmospheres or higher. Generally, high pressure, non-compliant balloons are formed from relatively inelastic materials such as oriented highly crystalline polyethylene terephthalate (PET) films. Such PET films provide high tensile strength, and may be used to form balloons with thin walls having high burst pressures. However, balloons formed from PET and similar materials having a high strength relative to wall thickness tend to be more susceptible to puncture. Balloons formed from PET also tend to be stiffer than balloons made from other more compliant materials. The stiffness of the deflated balloon directly affects its “trackability,” i.e., its ability to traverse sharp turns or branches of the vessels or body cavities through which the balloon must pass. Balloons having more flexible walls generally provide better trackability.
The term “semi-compliant” is used herein to describe a balloon that exhibits a moderate degree of expansion when pressurized from its operating pressure (e.g. the pressure at which the balloon reaches its nominal diameter) to its rated burst pressure. In some applications a semi-compliant balloon may be more desirable than a non-compliant balloon. Semi-compliant balloons tend to be less stiff than semi-compliant balloons, resulting in better trackability. Semi-compliant balloons may also provide better puncture resistance than non-compliant balloons. Thus, a practitioner may prefer a semi-compliant balloon over a non-compliant balloon in procedures where the balloon must be used to expand a hard or calcified stenosis or where the balloon must be threaded through small diameter blood vessels, and/or where the balloon has to traverse a torturous path. In some instances, a semi-compliant dilation balloon may be used to pre-dilate a stenosis before stent placement. A practitioner may also prefer a semi-compliant dilation balloon over a non-compliant balloon for stent placement and/or for post-stent dilation.
Dilation balloons are often used to open or expand open body spaces restricted by tough tissues such as strictures, scarring or calcified areas. In these applications medical dilation balloons having high operating and burst pressures may be required. For example, dilation balloons are used in angioplasty, a procedure in which the balloon may be used to expand a stenoic lesion. In these applications it is desirable to make the outer wall of the dilation balloon as thin as possible while still maintaining the required pressure rating or burst strength. It is also desirable that the balloon exhibit a high degree of puncture resistance.
In order to reduce the profile of the balloon, dilation balloons may be formed with pleated walls. When the balloon is deflated (i.e., before or after inflation), these pleats are folded over, wrapped and/or rolled around the long axis of the balloon. Consequently, the thinner the wall material of the balloon, the smaller the diameter of the balloon-catheter assembly. A smaller diameter may be used with a smaller introducer, reducing patient discomfort. A smaller diameter also facilitates passage of the deflated balloon through narrow vessels, lumens or cavities of the body prior to deployment.
Semi-compliant balloons may be produced from materials such as nylon which is softer than PET and provides moderate compliance and improved trackability. However, the tensile strength of nylons suitable for fabricating medical dilation balloons is typically less than that of PET. Thus, a dilation balloon formed from a nylon or similar semi-elastic material would require thicker walls in order to achieve the same burst pressures as PET dilation balloons. This in turn increases the diameter of the balloon catheter assembly and the size of the introducer used in the procedure. Thus, there exists a need for dilation balloons having a moderate level of compliance, puncture resistance, high burst pressures and thin walls.